Lignocellulosic material in fiber form is in wide commercial use as a raw material used for the manufacture of paper and other paper products. In papermaking, wood fibers usually are treated by combining them with other additives, and the fibers are then processed into a network of wood fibers, which can constitute a paper or other thin sheet of fibrous material. A variety of paper and paper products are decolored, namely, whitened or brightened, before they are marketed. The manufacture of decolored paper products usually includes process phases of pulping, bleaching, and papermaking. In order to produce strong and bleachable paper-making fibers, the wood or pulp fibers usually are treated to remove lignin, and commonly, the initial part of this treatment takes place in a digester in the presence of chemicals such as sodium hydroxide and sodium sulphide (to produce a kraft pulp) or sulphites, usually sodium or magnesium, (to produce a sulphite pulp), thus producing chemical pulps. The removal of lignin is referred to as delignification. The lignin content of wood pulps usually can be measured by a permanganate oxidation test according to a Standard Method of the Technical Association Of The Pulp And Paper Industry (TAPPI), and can be reported as a Kappa Number. The chemical pulp from the digester still contains an appreciable amount of residual lignin at this stage, and in some cases is suitable for making construction or packaging paper without further purification. For most applications, such as the manufacture of printing, writing, and sanitary papers, for example, the pulp usually is too dark in color and must be brightened by bleaching before papermaking. The paper product brightness is mainly dictated by pulp brightness provided before papermaking. There are some modifications in stock preparation which can alter paper brightness to some extent, such as filler, sizing, whitening agent, dying, and so forth. However, pulp brightness often is a primary factor or limitation on the paper brightness which can be ultimately obtained in paper products derived from the pulp.
Unbleached pulps can exhibit a wide range of brightness values. It is generally understood that chromophoric groups on the lignin are primarily responsible for pulp color. See, e.g., G. A. Smook, Handbook For Pulp And Paper Technologists, Chapter 11: Bleaching, 163-164, Tappi Pr. (1992), which is incorporated by reference in its entirety herein. Heavy metal ions (e.g., iron, copper) are also known to form colored complexes with phenolic groups of lignin. Extractive materials also can contribute to the color of mechanical pulps made from resinous woods. To produce high-quality stable paper pulps having a more permanent whitened effect, bleaching methods that decolor pulp have been used. However, use of large quantities of bleaching agents to obtain a specified level of decoloring is often undesirable.
Conventional methods for bleaching pulp have used a variety of multi-stage bleaching sequences, including multiple stages, or steps, with or without washing between the stages. Traditionally, the bleaching sequences have been based on the use of chlorine and chlorine-containing compounds, in one form or another. Some of the chlorine-containing compounds that have been used are chlorine, denoted “C” as a shorthand designation used in the industry, chlorine dioxide, denoted “D”, and hypochlorites, denoted “H”, usually sodium hypochlorite. Chlorine, with or without admixture of chlorine dioxide, has been commonly employed for the bleaching of chemical pulp, followed by alkaline (caustic) extraction, denoted “E,” of the chlorine-treated pulp in an aqueous alkaline medium, which together are denoted C-E. Oxygen, hypochlorite, or oxygen generators such as peroxide, also have been used as a bleaching agent in the bleaching stage, in combination with the alkaline extraction stage, or both. Washing units have been used after bleaching stages and between the oxidation and extraction stages. Additional information on conventional bleaching systems and process designs thereof is shown, for example, in the cited section of the above-referenced Handbook For Pulp And Paper Technologists. 
Enzymes also have been studied for their use in the treatment of wood fibers to degrade lignocellulosic material. The wood fibers used to make paper products usually include cellulose, hemicellulose, and lignin. The amounts of these three constituents present in the wood fiber can depend on the fiber source and their amounts in paper products made with the fiber can further depend on the manufacturing process used. The cohesion of the plant cell wall is primarily due to the presence of its principal components; the crystalline polymer, cellulose, and the three-dimensional macromolecule, lignin, comprising a lignocellulosic material. These components are embedded in a matrix of pectic and hemicellulotic polysaccharides of various nature. It is generally accepted that the relations that exist between these different polymers are established through linkages of different chemical nature. For instance, blocks of lignin are associated through hemicellulose chains. The hemicellulose, another major component of lignocellulosic material, consists largely of 4-O-methylglucuronoxylan, which includes the β-1,4-linked polymer of D-xylose, and herein referred to as xylan. Generally, hardwood pulps contain larger amounts of xylan than do softwood pulps. Such xylan can be enzymatically hydrolyzed to xylose by an endo-xylanase, β-1,4-D-xylan xylanohydrolase, denoted EC 3.2.1.8, and a xylosidase, β-1,4-D-xylohydrolase. Xylanases per se have been mentioned for xylan degradation in the pulp and paper industry in the pretreatment of pulps before chemical bleaching. See, e.g., F. I. J. Pastor et al., “Xylanases: Molecular Properties And Applications,” Industrial Enzymes, 65-67, 74-79, 2007. Further, untreated wood also generally contains some amount of pitch, which is typically located in parenchyma cells and on the surfaces of the fiber. Based on solubility in ethyl ether values, pitch may comprise, for example, from about 0.7 to about 2.4 weight percent of hardwoods, such as beech and white birch, and from about 0.7 to about 4.3 weight percent of softwoods such as eastern hemlock and jack pine, based on the total weight of unextracted (oven-dry) wood. The addition of lipase and a cationic polymer to a cellulosic slurry for pitch deposit control has been mentioned. See, e.g., U.S. Pat. No. 5,256,252, which is incorporated by reference in its entirety herein.
The present inventors have recognized a need to control bleach-interfering constituents of wood fiber by a pretreatment of the fibers before bleaching with a combination of agents that can increase pulp brightness obtained from bleaching in a way not predicted from the effects of the individual components of the pretreatment composition.
Enzymes are a significant element of many industrial processes such as paper production, leather preparation, waste treatment, and processing of biomass into fuel. While enzymes can appreciably increase the rate of chemical reactions, finding the right conditions to realize enzyme optimization has proved to be difficult. As a consequence, when enzymes are used they are used in a manner that yields sub-optimal enzymatic activity. That inefficiency causes the need to use additional, often costly, enzymes, as well as longer production times and additional energy inputs. Accordingly, there exists a need for enhancing the activity of enzymes to provide more efficient and cost-effective processes.